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2004
Fortunato, Elvira, Luı́s Pereira, Hugo Águas, Isabel Ferreira, and Rodrigo Martins. "Flexible position sensitive photodetectors based on a-Si: H heterostructures." Sensors and Actuators A: Physical. 116 (2004): 119-124. Abstract
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Fortunato, E., Pereira Águas Ferrira Martins L. H. I. "Flexible position sensitive photodetectors based on a-Si:H heterostructures." Sensors and Actuators, A: Physical. 116 (2004): 119-124. AbstractWebsite

This work describes the fabrication and characterization of an improved version of large area (5mm×80mm with an active length of 70mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide-Kapton® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12A/W at 500nm and a non-linearity of ±10% over 70mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature. © 2004 Elsevier B.V. All rights reserved.

Goulão, Miguel, and Fernando Brito Abreu. "Formalizing Metrics for COTS." International Workshop on Models and Processess for the Evaluation of COTS Components (MPEC 2004) at ICSE 2004. Eds. Eric Dubois, and Xavier Franch. Edimburgh, Scotland: IEE, 2004. 37-40. Abstract
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Pereira, LuÍs, Isabel Ferreira, Rodrigo Martins, Hugo Águas, Elvira Fortunato, Leandro Raniero, S. Zang, and L. Boufendi. "Growth of Polymorphous/Nanocrystalline Silicon Films Deposited by PECVD at 13.56 MHz." Materials Science Forum. 455 (2004): 532-535. Abstract
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Raniero, Leandro, Rodrigo Martins, Hugo Águas, S. Zang, Isabel Ferreira, Lu{\'ıs Pereira, Elvira Fortunato, and L. Boufendi. "Growth of polymorphous/nanocrystalline silicon films deposited by PECVD at 13.56 MHz." Materials Science Forum. Vol. 455. Trans Tech Publications, 2004. 532-535. Abstract
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Fortunato, E., A. Pimentel, L. Pereira, A. Goncalves, G. Lavareda, H. Aguas, I. Ferreira, CN Carvalho, and R. Martins. "High field-effect mobility zinc oxide thin film transistors produced at room temperature." Journal of non-Crystalline solids. 338 (2004): 806-809. Abstract
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Fortunato, E., Pimentel Pereira Gonçalves Lavareda Águas Ferreira Carvalho Martins A. L. A. "High field-effect mobility zinc oxide thin film transistors produced at room temperature." Journal of Non-Crystalline Solids. 338-340 (2004): 806-809. AbstractWebsite

In this paper we present the first results of thin film transistors produced completely at room temperature using ZnO as the active channel and silicon oxynitride as the gate dielectric. The ZnO-based thin film transistors (ZnO-TFT) present an average optical transmission (including the glass substrate) of 84% in the visible part of the spectrum. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 1.8 V. A field effect mobility of 70 cm2/Vs, a gate voltage swing of 0.68 V/decade and an on-off ratio of 5×105 were obtained. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT very promising for the next generation of invisible and flexible electronics. © 2004 Elsevier B.V. All rights reserved.

Fortunato, E., A. Pimentel, L. Pereira, A. Goncalves, G. Lavareda, H. Aguas, I. Ferreira, CN Carvalho, and R. Martins. "High field-effect mobility zinc oxide thin film transistors produced at room temperature." Journal of non-Crystalline solids. 338 (2004): 806-809. Abstract
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Fortunato, E., Pimentel Gonçalves Marques Martins A. A. A. "High mobility nanocrystalline indium zinc oxide deposited at room temperature." Materials Research Society Symposium Proceedings. Vol. 811. 2004. 437-442. Abstract

In this paper we present results of indium doped zinc oxide deposited at room temperature by rf magnetron sputtering, with electron mobility as high as 60 cm2/Vs. The films present a resistivity as low as 5×10 -4 Ωcm with an optical transmittance of 85%. The structure of these films look-like polymorphous (mixed of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns (no clear peak exists) with a high smooth surface, as detected from SEM micrographs, highly important to ensure long life time when used in display devices.

Fortunato, E., V. Assuncao, A. Goncalves, A. Marques, H. Aguas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "High quality conductive gallium-doped zinc oxide films deposited at room temperature." Thin Solid Films. 451 (2004): 443-447. Abstract
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Fortunato, E.a, Assunção Gonçalves Marques Águas Pereira Ferreira Vilarinho Martins V. a A. a. "High quality conductive gallium-doped zinc oxide films deposited at room temperature." Thin Solid Films. 451-452 (2004): 443-447. AbstractWebsite

Transparent and highly conducting gallium-doped zinc oxide films were successfully deposited by rf sputtering at room temperature. The lowest resistivity achieved was 2.6×10-4 Ω cm for a thickness of 1100 nm (sheet resistance ≈1.6 Ω/sq), with a Hall mobility of 18 cm2/Vs and a carrier concentration of 1.3×1021 cm-3. The films are polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. A linear dependence between the mobility and the crystallite size was obtained. The films present a transmittance in the visible spectra between 80 and 90% and a refractive index of approximately 2, which is very close to the value reported for bulk material. © 2003 Elsevier B.V. All rights reserved.

Fortunato, E., V. Assuncao, A. Goncalves, A. Marques, H. Aguas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "High quality conductive gallium-doped zinc oxide films deposited at room temperature." Thin Solid Films. 451 (2004): 443-447. Abstract
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Barquinha, P., L. Pereira, H. Aguas, E. Fortunato, and R. Martins. "Influence of the deposition conditions on the properties of titanium oxide produced by rf magnetron sputtering." Materials science in semiconductor processing. 7 (2004): 243-247. Abstract
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Marat-Mendes, J. N., E. R. Neagu, R. Martins, E. Fortunato, I. Ferreira, and C. Dias. "The influence of water on direct current conductivity of cork." Advanced Materials Forum Ii. Vol. 455-456. 2004. 446-449. Abstract
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Neagu, R. M., E. R. Neagu, C. J. Dias, J. N. Marat-Mendes, R. Martins, E. Fortunato, I. Ferreira, and C. Dias. "Isothermal and non-isothermal DC measurements to analyze space charge behavior in polyamide 11." Advanced Materials Forum Ii. Vol. 455-456. 2004. 450-454. Abstract
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Fernandes, M.a, Vieira Rodrigues Martins M. a I. a. "Large area image sensing structures based on a-SiC:H: A dynamic characterization." Sensors and Actuators, A: Physical. 113 (2004): 360-364. AbstractWebsite

In recent works large area hydrogenated amorphous silicon p-i-n structures with low conductivity doped layers were proposed as single element image sensors. The working principle of this type of sensor is based on the modulation, by the local illumination conditions, of the photocurrent generated by a light beam scanning the active area of the device. In order to evaluate the sensor capabilities is necessary to perform a response time characterization. This work focuses on the transient response of such sensor and on the influence of the carbon contents of the doped layers. In order to evaluate the response time a set of devices with different percentage of carbon incorporation in the doped layers is analyzed by measuring the scanner-induced photocurrent under different bias conditions. © 2004 Elsevier B.V. All rights reserved.

Alendouro, M. S. J. G. a, R. C. C. a Monteiro, C. F. M. L. a Figueiredo, R. M. S. a Martins, R. J. C. a Silva, M. C. b Ferro, and M. H. V. b Fernandas. "Microstructural characterization and properties of a glass and a glassceramic made from municipal incinerator bottom ash." Materials Science Forum. 455-456 (2004): 827-830. AbstractWebsite

A glass was made using bottom ash produced by a Portuguese municipal solid waste (MSW) incinerator. The bottom ash was the single batch material used in the formation of the glass, which was obtained through a conventional melt-quenching method. The glass was then converted to glass-ceramic for further recycling to construction materials. After submitting the glass samples to several heat treatments, between 820 and 1050°C and during different times, it was verified that the optimum heat treatment schedule for the ceramization of the glass was at 1000°C for 10h, as confirmed by microstructural observation and by X-ray diffraction. The major crystalline phases precipitated in the glass-ceramic were wollastonite (CaSiO3) and diopside (Ca(Mg,Al)(Si,Al)2O6). Microstructural analysis of the glass-ceramic revealed that the crystalline phases were present as dendrites and fiber-like structures that were homogeneously distributed in the material. The glassceramic showed good mechanical properties with a hardness of 5.6 MPa and a bending strength of 101 MPa. This material had a density of 2.8 gcm-3 and a thermal expansion coefficient of 9.10-6°C-1. The glass and the glass-ceramic showed an excellent chemical stability against leaching in acidic solution and in alkaline solution. In summary, both the glass and the glass-ceramic have good chemical and mechanical properties and can, therefore, be applied as construction materials.

Águas, Hugo, Lu{\'ıs Pereira, Leandro Raniero, Elvira Fortunato, and Rodrigo Martins. "MIS Photodiodes of Polymorphous Silicon Deposited at Higher Growth Rates by 27.12 MHz PECVD Discharge." Materials Science Forum. Vol. 455. Trans Tech Publications, 2004. 73-76. Abstract
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Hettmann, T., R. A. Siddiqui, C. Frey, T. Santos-Silva, MJ Romão, and S. Diekmann. "Mutagenesis study on amino acids around the molybdenum centre of the periplasmic nitrate reductase from Ralstonia eutropha." Biochemical and Biophysical Research Communications. 320 (2004): 1211-1219. Abstract
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Fortunato, E., A. Gonçalves, A. Marques, A. Viana, H. Águas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180 (2004): 20-25. Abstract
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Fortunato, E.a, Gonçalves Marques Viana Águas Pereira Ferreira Vilarinho Martins A. a A. a. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180-181 (2004): 20-25. AbstractWebsite

Gallium-doped zinc oxide (GZO) thin films have been deposited onto polyethylene naphthalate (PEN) substrates by r.f. magnetron sputtering at room temperature. The influence of the film thickness (from 70 to 890 nm) on the electrical, structural and morphological properties are presented. The lowest resistivity obtained was 5 × 10-4 Ω cm with a Hall mobility of 13.7 cm2/Vs and a carrier concentration of 8.6 × 1020 cm-3. These values were obtained by passivating the surface of the polymer with a thin silicon dioxide, so preventing the moisture and oxygen permeation inside the film. © 2003 Elsevier B.V. All rights reserved.

Fortunato, E., A. Goncalves, A. Marques, A. Viana, H. Aguas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180 (2004): 20-25. Abstract
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Fortunato, E., P. Barquinha, A. Pimentel, A. Goncalves, L. Pereira, A. Marques, and R. Martins. "Next generation of thin film transistors based on zinc oxide." Integration of Advanced Micro-and Nanoelectronic Devices-Critical Issues and Solutions. Eds. J. Morais, D. Kumar, M. Houssa, R. K. Singh, D. Landheer, R. Ramesh, R. M. Wallace, S. Guha, and H. Koinuma. Vol. 811. Materials Research Society Symposium Proceedings, 811. 2004. 347-352. Abstract
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Fortunato, E., Barquinha Pimentel Gonçalves Pereira Marques Martins P. A. A. "Next generation of thin film transistors based on zinc oxide." Materials Research Society Symposium Proceedings. Vol. 811. 2004. 347-352. Abstract

We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.

Fernandes, M.a, Vieira Martins M. a R. b. "Novel structure for large area image sensing." Sensors and Actuators, A: Physical. 115 (2004): 357-361. AbstractWebsite

This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device. © 2004 Elsevier B.V. All rights reserved.

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